How many times have you started a diet, but felt so sluggish and cranky after a few days that you threw in the towel? You're not alone. Dieting can deplete energy, because you are cutting back on calories, your body's source of fuel. But it is possible to lose weight and still feel good. Here's what I tell my clients about the healthy way to diet:

Eat More Meals, Not Fewer

When you don't eat breakfast, you overeat at lunch. And while that may add up to the same number of calories (no breakfast + big lunch = breakfast + smaller lunch), larger meals zap more of your energy because they put greater stress on your digestive system. The reason? Approximately 10 percent of your daily energy supply is used in the digestive process. When you overeat, that process goes into overdrive, demanding even more energy to break down the food and leaving your body drained. (Think of how sleepy you feel after a Thanksgiving feast.) Smaller meals several times a day can help you conserve energy.

Yes, there are studies that now say people may not need as much water as previously thought. But that's not true for dieters. In order to lose weight without feeling sluggish, you need your H2O. Here's why: Water regulates your body temperature, removes waste, transports nutrients to cells, cushions joints, and protects organs. Without enough H2O in your body, it becomes increasingly difficult for your system to operate — leaving you tired and even light-headed. Another point: It's easy to mistake the midafternoon munchies for hunger, when dehydration could be the culprit. Don't believe me? Next time the 3:00 snack attack occurs, pour yourself a tall glass of water instead of reaching for chips. Even if you still want the food, I'll bet you eat less after drinking a glass of water.

Get Moving

Exercise is a key part of any diet plan, not only because it burns calories, but because it keeps your energy up even when you're not working out. Anything that elevates your heart rate — walking, biking, playing Frisbee — circulates more oxygen to your lungs. The better your circulation is, the more energy you'll have.

In fact, not exercising does more damage to a weight-loss plan than many women realize. After age 20, women lose 0.5 to 0.7 pounds of muscle each year. That's five to seven pounds lost each decade! What replaces the muscle? Fat. So you're not shedding weight — just developing a weaker, less fit body. Everything becomes more difficult: carrying groceries, holding a child, taking out the trash. Exercise — especially strength training — helps ensure that you don't just get slim, you also get strong.

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Monitor Sleep and Stress Levels

Sleep is a critical element of successful weight loss, since it's your body's chance to recharge. Too little sleep doesn't just make you sluggish, it can also cloud your thinking, leaving you more susceptible to temptation when you pass the donut shop on the way to work.

Controlling stress is also important (it can wreak havoc on a diet in more ways than chocolate). Did you know that stress can actually induce a physiological change that makes losing weight harder? It causes your body to release a hormone called cortisol, which may encourage fat cells to build up in your abdomen as part of the stress response. So take a deep breath, get some sleep, and relax.

Commit to One Week of Dieting

Bottom line: Weight loss is the long-term key to feeling more energetic. If you're overweight, your organs and muscles have to support a larger mass than nature planned, meaning they must work harder to perform everyday activities. So even if you're a veteran of many failed diets, try again. This time, just commit for one week. The first few days will be tough — but after seven days, you'll start to see a difference. You'll also feel stronger and more energized — and you may even be ready to commit to week two.